RE: DB memory parameter question
- From: Noveljic Nenad <nenad.noveljic@xxxxxxxxxxxx>
- To: "niall.litchfield@xxxxxxxxx" <niall.litchfield@xxxxxxxxx>, Stefan Koehler <contact@xxxxxxxx>
- Date: Wed, 13 Feb 2019 08:25:46 +0000
By the way, using AMM can be detrimental to the system performance on Solaris.
Further, it isn’t recommended for use with Solaris x86, see
https://www.oracle.com/technetwork/articles/systems-hardware-architecture/using-dynamic-intimate-memory-sparc-168402.pdf
Nenad
https://nenadnoveljic.com/blog/
From: oracle-l-bounce@xxxxxxxxxxxxx <oracle-l-bounce@xxxxxxxxxxxxx> On Behalf
Of niall.litchfield@xxxxxxxxx
Sent: Mittwoch, 13. Februar 2019 09:09
To: Stefan Koehler <contact@xxxxxxxx>
Cc: Backseat DBA <backseatdba@xxxxxxxxx>; oracle-l-freelist
<oracle-l@xxxxxxxxxxxxx>
Subject: Re: DB memory parameter question
Not surprisingly I agree entirely with Stefan (although I suspect many people
will be in the ASMM position because not many DBAs get that much time to
understand applications any more). I see you are on 12.2 - if you do go down
the PGA_AGGREGATE_TARGET route then, from 12.1 by doing this you are also
effectively setting PGA_AGGREGATE_LIMIT
https://docs.oracle.com/database/121/REFRN/GUID-E364D0E5-19F2-4081-B55E-131DF09CFDB3.htm#REFRN10328
which is a hard limit on PGA usage and can lead to PX slaves and/or sessions
being aborted. At this point, you will start to discover how your application
uses memory again :)
On Wed, Feb 13, 2019 at 7:24 AM Stefan Koehler
<contact@xxxxxxxx<mailto:contact@xxxxxxxx>> wrote:
Hello Jeff,
here is my humble opinion about this.
AMM (memory_target): Never ever use it except for some playground databases for
yourself. You already mentioned the limitations with huge pages and in addition
the SHM granules are deflated/inflated.
ASMM (sga_target): It caused many problems when it was implemented first but
nowadays it is pretty common and stable. However be aware that you still can
run into issues with it (e.g. current example:
https://twitter.com/jolliffe/status/1094195271448186881). You can use huge
pages and it is static.
PGA (pga_aggregate_target): Usage is common standard nowadays however you may
need to tweak the underscore parameters a little bit if you need huge memory
allocations for a work area (e.g.
http://www.soocs.de/public/research/150731_auto_pga_max_workarea.txt).
Summary: IMHO always use manual memory management for SGA and Auto PGA whenever
possible. Use ASMM and Auto PGA if you don't know the memory requirements for
the application. Never use AMM. :)
Best Regards
Stefan Koehler
Independent Oracle performance consultant and researcher
Website: http://www.soocs.de
Twitter: @OracleSK
Jeff Chirco <backseatdba@xxxxxxxxx<mailto:backseatdba@xxxxxxxxx>> hat am 12.
Februar 2019 um 20:05 geschrieben:
Ok from what I have read in various documents and experienced it is not a
good idea to use memory_target anymore, or at least on databases with large
memory. Plus if you want to use huge pages you can’t. What about
sga_target, sga_max_target, and pga_aggregate_target? Do I set those or
still no and just set each individual SGA memory area?
I recently migrated over from Windows to Oracle Linux, running 12.2.0.1 EE.
Thanks
Jeff
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Niall Litchfield
Oracle DBA
http://www.orawin.info
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